I sometimes help people with windows problems, however I point to them that they could live with less problems and when they had one I wouldn't ask them to compensate my help with anything... I actually like helping people, but it frustrates me to no end that people who don't do anything they couldn't do with any other OS refuse to try out Linux, which I've installed to several not very computer savvy folks and received way fewer help requests after and only positive feedback of the system in comparison (people who like/want/need to use software not available for Linux are not the subject of this mini-rant part).
Anyway, I like helping people, but I don't normally promise to people that I will be there for them any time, any day for any problem - however I have committed myself to helping people who have decided to try Linux because of what I've told them. Part of my "selling speech" actually includes supporting them as long as they have the Linux, without compensation.
I like to think of it as my small contribution to Linux and Open Source community.